Process for stabilizing the PH of a pulp suspension and for producing paper from the stabilized pulp

ABSTRACT

The invention relates to a process for stabilizing the pH of a pulp suspension with buffering agents and to a process for producing paper from a stabilized pulp suspension. The alkalinity of the pulp suspension is increased by a combination of an alkali metal hydroxide feed and a carbon dioxide feed. Said feeds provide a significant buffering effect which stablilizes the pH of said pulp suspension for the paper making process.

The invention relates to a process for stabilizing the pH of a papermaking pulp suspension with buffering agents and to a process forproducing paper from such a stabilized pulp suspension.

During the last ten to fifteen years many paper makers have convertedtheir processes from acidic to neutral pH for a number of reasons, e.g.to gain increased strength and to be able to use calcium carbonate,CaCO₃, as a filler. The expression “neutral pH” corresponds in theseprocesses to a pH in the short circulation of approximately 7–8.5, mostpreferably 7–8. This applies to paper produced from chemical, mechanicaland recycled pulp, bleached or unbleached.

If the paper making pulp is acidic when entering the stock preparationand the short circulation is run at a neutral or alkaline pH, thetraditional way of raising and controlling the pH is to add sodiumhydroxide, NaOH. NaOH is, however, a very strong base, which means thatonly small amounts are needed for pH adjustments. Any over-dosage willcause a too big pH increase, which means that it is difficult to performthe pH adjustment in a controlled way. This is due to the low inherentbuffering ability of a pulp suspension. The paper maker could end up ina situation with varying pH of the entering pulp, which has a negativeimpact on paper quality and paper machine runnability.

Through the stock preparation and the short circulation a number ofpaper chemicals and dilution waters are added, some of which are acidicand therefore decrease the pH of the pulp. The paper maker couldtherefore end up with a too low pH in the short circulation and would beonce again forced to pH adjust using NaOH. The pH may also change atrefining or in storage towers.

If the paper making pulp is alkaline instead when entering the stockpreparation and if the short circulation is run at a neutral or alkalinepH, there is naturally no need to use any NaOH for pH control. The papermaker must however make sure that the pH is high enough to avoid endingup with too low a pH after addition of acidic paper chemicals.

In the prior art one way of avoiding ending up with too low pH valueshas been to add dissolved sodium bicarbonate, NaHCO₃, to the pulp. TheNaHCO₃ dissociates in the pulp suspension forming bicarbonate ions, HCO₃⁻, which have a buffering effect and therefore counteract any pHdecrease. NaHCO₃ is a solid powder, which is generally supplied in socalled big-bags, and the paper mill needs space for handling, equipmentfor dissolving and tanks for storage. The NaHCO₃ is messy to work with,when in contact with moisture or water.

In the non-acidic sizing of paper with alkylketene dimers bicarbonateions have been used to catalyze the reaction between the alkylketenedimers and the cellulose. According to U.S. Pat. No. 5,378,322 thebicarbonate ions may be generated by dissociation of carbon dioxide CO₂in the aqueous pulp.

Carbon dioxide is a gas, which easily dissolves under alkalineconditions, e.g. in water or a pulp suspension forming carbonic acidand/or bicarbonate ions according to the reaction:CO₂+H₂O<=>H₂CO₃<=>H⁺+HCO₃ ⁻At a high pH, especially greater than 10, the predominant reaction isCO₂+OH⁻<=>HCO₃ ⁻

In the recycling of gypsum-containing waste or broke paper theaccumulation of calcium sulfate poses a problem since the solubilizedcalcium sulfate may precipitate and disturb the paper making process.According to U.S. Pat. No. 5,262,006 this problem may be overcome byadding carbonate ions and/or bicarbonate ions to the aqueous pulpsuspension and by adjusting the pH to an alkaline value to precipitatethe calcium as calcium carbonate. The bicarbonate ions may be created insitu for example by first adding a suitable soluble metal hydroxide andthen adding carbon dioxide. According to the Patent, the calciumcarbonate generation from calcium sulfate with carbon dioxide requires aclose control of the pH since carbon dioxide has the effect of loweringthe pH so that there is a risk of the pH becoming too low for thecarbonation process.

Carbon dioxide has also been used for the pH control of pulpsuspensions, for instance, in a process described in EP Patent 0 281273, wherein gaseous carbon dioxide is introduced to adjust and maintainthe pH at a value which is preferably between 7.0 and 5.5.

Thus, in the prior art carbon dioxide has been used to createbicarbonate ions for its catalyzing, carbonating or pH lowering effect.However, a paper maker also has the need to obtain a stable pH so thatchemical additions and various processing steps do not cause an unwantedfluctuation of the pH.

An object of the present invention is thus to provide a pH stabilizationof aqueous pulp suspensions.

Another object of the invention is to provide a paper making pulpsuspension having an increased alkalinity, i.e. a resistance to pHchange.

A further object of the invention is to provide a technicallyadvantageous process for buffering a pulp suspension.

An object is also to provide a pulp suspension having a controlled pHwhich is maintained at a desired level.

An object of the invention is also to provide a process for producingpaper from a pulp suspension having a stabilized pH.

The invention according to the present application is defined in theappended claims, the contents of which are included herein by reference.

Consequently, the present invention relates to a process for stabilizingthe pH of a pulp suspension, wherein the alkalinity of a paper makingpulp suspension is increased by adding thereto a combination of analkali metal hydroxide feed and a carbon dioxide feed which feedssubstantially counter each other's pH changing effect, said feeds beingprovided in an amount sufficient to achieve a significant bufferingeffect of said pulp suspension for paper making.

The feeding of a hydroxide and carbon dioxide in substantiallycountering amounts increases the level of alkalinity forming ions in thesuspension without actually affecting its pH. Increasing the alkalinitystabilizes the suspension against pH fluctuations caused by subsequentadditions of acidic or basic fluids and provides a stable pH throughoutthe succeeding steps.

Alkalinity is a measurement of “acid resistance”, i.e. the content ofbuffering ions in a liquid or pulp suspension, which counteracts pHdecrease at addition of hydrogen ions, H⁺. One way of expressingalkalinity is the amount of HCO₃ ⁻ and CO₃ ²⁻ ions in grams per liter.When a combination of hydroxide and carbon dioxide is used according tothe present invention, the alkalinity of the pulp suspension is raised,thus creating larger “acid resistance”.

The hydroxide used according to the invention should preferably be addedprior to the addition of the carbon dioxide to ensure that the carbondioxide is added under alkaline conditions.

The “amount sufficient to achieve a significant buffering effect” shouldbe taken as meaning an amount providing a substantial and recognizablebuffering effect in the pulp suspension. The amount normally variesdepending on the characteristics of the pulp and on the conditions oftreatment. A person skilled in the art will be able to calculate therequired amount based on his general knowledge or by simple tests madeon the actual pulp suspension, as indicated, for example in Example 9 ofthis specification.

Typically the amount of NaOH in the buffering combination will bebetween about 0.5 and 5 kg NaOH/ton dry cellulose and the amount ofcarbon dioxide in said combination will be between about 0.5 and 5 kgCO₂/ton dry cellulose. A typical buffering combination would includeabout 2 to 3 kg of NaOH and CO₂ per ton of dry cellulose. It is withinthe scope of the present invention to use more or less than the abovementioned amounts of both components, but in general it will beuneconomical to use more than what is required for a desired bufferingaction.

It is clear that the excess of either NaOH or CO₂ which is additionallyused for pH adjusting purposes may significantly exceed the aboveamounts which provide the buffering effect.

The buffering effect obtained by the addition of NaOR and CO₂ in thisway corresponds to the one obtainable by an addition of dissolved NaHCO₃but it has the advantage that the space consuming and messy handling ofsolid NaHCO₃ is avoided. Sodium hydroxide, on the other hand, is achemical which is abundantly available in the paper mill since it isused for many other purposes. Carbon dioxide gas may be generated onsite or may be bought as desired. Feeding of carbon dioxide into thesuspension is technically clean and easy.

A further advantage resides in that the hydroxide and carbon dioxideused according to the present invention may serve the dual purpose ofincreasing the alkalinity and of adjusting the pH. Thus, according to apreferred embodiment of the invention, the pH of said pulp suspension isincreased by adding an excess of alkali metal hydroxide such as aqueoussodium hydroxide or decreased by adding an excess of carbon dioxide.

The carbon dioxide is preferably in gaseous form, although it may beadded as an aqueous liquid by dissolving gaseous or solid carbon dioxidein water. The hydroxide and carbon dioxide may be combined prior tofeeding to the pulp suspension although it is preferred to feed themdirectly into the pulp circulation system such as to a pipe leading to astock preparation tank.

The pulp suspension is preferably buffered by said combination to a pHbetween about 7 and 9.

According to the preferred embodiment of the invention the alkalinity ofthe pulp suspension is increased by providing a substantially equalmolar amount of alkali metal hydroxide and dissolved carbon dioxide,said amount being sufficient to provide a significant buffering effectat about pH 8.

The pulp suspension may be bleached or unbleached chemical or mechanicalpulp although the preferred pulp is bleached chemical pulp.

Calcium carbonate may advantageously be used as a filler for the pulp,since the stabilized pH will ascertain that the filler remains in solidform in the suspension. A fluctuation of the pH down to 6 or 5.5, forinstance due to an inflow of circulating white water at such a pH, mightdissolve the carbonate filler. Such an undesirable effect will beeffectively prevented by the buffering action of the present invention.

The present invention also relates to a process for producing paper,said process comprising the steps of

-   -   providing a paper making pulp suspension;    -   increasing the alkalinity of said pulp suspension by adding        thereto a combination of an alkali metal hydroxide feed and a        carbon dioxide feed which feeds substantially counter each        others pH changing effect, said feeds being provided in an        amount sufficient to achieve a substantial buffering effect of        said pulp suspension for paper making;    -   optionally adjusting the pH of said pulp suspension to a desired        value between 7 and 9 by adding an alkaline agent such as NaOH        or an acidic agent such as CO₂;    -   forming said pulp suspension into a web; and    -   drying said web to form paper.

The production of paper according to the present invention is performedin a conventional way in all other respects except for the increase ofthe alkalinity of the pulp prior to the short circulation. Such papermaking processes are well known in the art and it is not considerednecessary to describe them here in any greater detail.

The invention will now be illustrated with a few examples which shouldnot be considered as limiting the invention in any way.

EXAMPLE 1 (Reference Example)

In a partly integrated paper mill bales of fully bleached kraft marketpulp are introduced into a pulp slusher. The pH in the slusher isadjusted with aqueous NaOH to a pH of approximately 11.

After slushing, paper making chemicals and dilution water having anacidic effect are added to the slushed pulp suspension. As a consequenceof this, the pH of the pulp suspension decreases from pH 11 to about pH6.5–6.8. This pH is too low for the short circulation, which is run at apH level of 7–7.5. Thus, the pH is again adjusted by an addition ofaqueous NaOH.

Because of the strong basic action of NaOH it is difficult to achieve anexact pH control in this way. Over-dosing leads to a too high pH.

EXAMPLE 2

The process of Example 1 is changed in order to improve the situation,so that a combination of NaOH and CO₂ is added to the pulp slusher. Theamount of NaOH added to the suspension is substantially increasedcompared to the process of Example 1. A countering amount of Co₂ isadded to provide a pH of approximately pH 9.

After slushing, the same paper chemicals as in Example 1 are added tothe slushed pulp suspension. Because of the buffering effect of thecombined NaOH and CO₂, the acidic additions lower the pH only to pH 7.2.This is a suitable pH for the short circulation and there is no need forany pH control using NaOH.

EXAMPLE 3 (Reference Example)

In a paper mill a kraft pulp suspension having a pH of 5.1 is fed to astorage tower. Prior to the entry into the tower, the pH of the pulpsuspension is adjusted to pH 8 by an addition of aqueous NaOH into thepipe leading to the tower. The pulp suspension is fed from the storagetower to a refiner. At refining the pH decreases to about pH 6.

The low pH causes problems in the subsequent sizing of the pulp.

EXAMPLE 4

The process of Example 3 is repeated with the exception that instead offeeding only the required amount of NaOH into the pulp suspension, anexcess of NaOH is fed first into the pipe followed by feeding gaseousCO₂ into the pipe counteracting the excess NaOH. The resultingsuspension again has a pH of 8 when entering the storage tower.

From the storage tower the pulp is fed to the refiner. At refining thepH remains at about pH 8 and there are no problems at sizing.

EXAMPLE 5

In a laboratory trial a pulp suspension having a pH of 5.1 was used. ThepH of the pulp suspension was adjusted to pH 8 by using a) only NaOH andb) by using an excess of NaOH in combination with CO₂. The bufferingeffect of the suspension was tested with a strong acid (alum, pH 3.0).

The results are shown in Table 1 below.

TABLE 1 NaOH CO₂ alum pH¹ (ml) (g) pH² (ml) pH³ a) (NaOH) 5.1 2 — 8.0 16.4 b) (NaOH + 5.1 3 1 8.0 1 7.9 CO₂) ¹the pH of the initial pulpsuspension ²the pH after addition of NaOH/NaOH + CO₂ ³the pH afteraddition of acid

In the above process 1 ml of the aqueous NaOH corresponds to about 2.5kg/ton cellulose calculated on the dry weight basis; 1 g of CO₂similarly corresponds to about 2.5 kg/ton cellulose; and 1 ml of alumcorresponds to about 2.8 kg/ton cellulose.

The above results clearly show that the addition of countering amountsof NaOH and CO₂ stabilize the pH of the pulp suspension.

EXAMPLE 6 (Reference Example)

A pulp suspension was stored in a pulp storage tank in a pulp mill at apH of 5.5 to 6. The pulp was fed at this pH at a consistency of 3 to 4%to the paper mill via a press which increased the consistency to about10%. The pulp was fed at this consistency to the paper mill storage tankat a pH of 5.5 to 6.

White water from the paper machine was fed to the storage tank at a pHof 7.5 to 8. The paper was produced with CaCO₃ as filler. Some of thefiller circulated with the white water to the storage tank. Whenentering the storage tank the CaCO₃ in the white water dissolved as itmet the pulp suspension at pH 5.5 to 6.

The dissolving of the CaCO₃ caused loss of filler and in additionthereto the calcium ions increased the hardness of the water and causedprecipitations at unwanted positions.

From the storage tank the suspension was fed to a refiner. For improvingthe refining the pH of the pulp suspension was adjusted to 7.5 with NaOHbefore the refiner. Careful control of the NaOH feed was required toavoid dosing too much or too little.

In the refiner the pH decreased to 6 to 6.5 which meant increased energyconsumption at refining. The pH was too low for the sizing. Thus, the pHhad to be adjusted again for the sizing.

EXAMPLE 7 (Reference Example)

The process of Example 6 was repeated with the exception that aqueousNaHCO₃ was fed to the paper mill storage tank to obtain the desired pHof about 7.5 to 8. The CaCO₃ in the white water was not dissolved andthe problem with filler loss was resolved.

The pH of the feed to the refiner was about 7.5 and no NaOH was fed tothe suspension. However, in the refiner the pH decreased as before and apH adjustment with NaOH was required for sizing.

EXAMPLE 8

The process of Example 6 was repeated with the exception that NaOH andCO₂ were fed to the pipe leading to the paper mill storage tank. The pHwas adjusted to 8 and no loss of filler occurred in the storage tank.

The pH of the feed to the refiner was about 8 and no NaOH was fed to thesuspension. At refining the alkalinity of the suspension counteractedthe pH lowering effect in a sufficient degree to retain the pH at 7.5 to8.

There was no need for a pH adjustment for sizing. The pulp was used forthe production of paper with an excellent result.

EXAMPLE 9

A pulp suspension having a 10% consistency and a pH of 7.4 was dividedinto two lots, Pulp 1 and Pulp 2, respectively, weighing 2030 g each.The pH of the pulp suspension was adjusted on one hand with sulfuricacid (a 10% by weight aqueous solution of H₂SO₄) and on the other handwith gaseous carbon dioxide and a combination of 1 M sodium hydroxideand carbon dioxide gas.

The pH of Pulp 1 was adjusted to 6.2 with said sulfuric acid. The pH ofPulp 2 was adjusted to 6.2 by adding 15 ml sodium hydroxide and 1.02 gof carbon dioxide. The resulting pulp suspensions were titrated with 10%sulfuric acid to study their respective resistance to pH change.

The results are indicated in Table 2 below.

TABLE 2 Titration pH pH H₂SO₄ (kg/t) Pulp 1 Pulp 2 0 6.22 6.20 1.4 6.186.20 2.4 6.10 6.21 4.7 6.03 6.17 10.6 5.82 6.12

The sulfuric acid in Table 2 is indicatied in kg of 100% H₂SO₄ per tonof dry cellulose.

For the above adjustment of the pH and alkalinity of Pulp 2, NaOH wasadded in an amount of 2.9 kg/ton cellulose and CO₂ was used in an amountof 5.1 kg/ton cellulose. The CO₂ was used both for pH adjustment and tocounter the addition of sodium hydroxide.

The test shows that fairly small amounts of a combination of sodiumhydroxide and carbon dioxide provides an effective buffering action. Theabove final pH of 6.12 would render Pulp 2 fully useful for papermakingpurposes, while the final pH of Pulp 1 would be too low.

It is evident that the invention may be varied in a great number of wayswhich are obvious to those skilled in the art without deviating from thescope of the claims.

1. A process for stabilizing the pH of a pulp suspension at a desired pHlevel, comprising increasing the buffering ability of said pulpsuspension by adding thereto, in the stock preparation of a papermachine in a paper mill, a combination of an alkali metal hydroxide feedand a carbon dioxide feed, which cooperate to increase the pH of saidpulp suspension and to otherwise only counter each other's pH adjustingeffects without further separate uses of their respective intermediatepH adjusting effects, each of said feeds being added in an amountgreater than what would be required to only adjust the pH of thesuspension to the desired pH level, said feeds being provided in anamount sufficient to achieve a significant buffering effect of said pulpsuspension and to increase the pH of said pulp suspension and maintainthe pH at a desired level from the addition of the feeds throughout theshort circulation and formation of the paper on the paper machine. 2.Process according to claim 1, characterized in that the pH of said pulpsuspension is increased to a pH between about 7 and
 9. 3. Processaccording to claim 1, characterized in that said alkali metal hydroxideis aqueous sodium hydroxide and said carbon dioxide is gaseous carbondioxide.
 4. Process according to claim 1, characterized in that saidalkali metal hydroxide is fed to said pulp suspension prior to thefeeding of said carbon dioxide.
 5. Process according to claim 1,characterized in that the buffering ability of said pulp suspension isincreased by providing a substantially equal molar amount of alkalimetal hydroxide and dissolved carbon dioxide, said amount beingsufficient to provide a significant buffering effect at about pH
 8. 6.Process according to claim 1, characterized in that said pulp suspensionis chemical or mechanical pulp.
 7. Process according to claim 6,characterized in that said pulp suspension is a bleached chemical pulp.8. Process according to claim 1, characterized in that said pulpsuspension contains calcium carbonate filler.
 9. Process according toclaim 1, characterized in that said alkali metal hydroxide and carbondioxide feeds are added to said pulp suspension flowing in a pipeleading to a stock preparation tank.
 10. Process according to claim 1,characterized in that said alkali metal hydroxide and said carbondioxide are combined prior to feeding to the pulp suspension. 11.Process according to claim 1, wherein said paper making pulp suspensionis provided by adding water to bales of pulp or adding water to pulp ofincreased consistency coming from a pulp mill.
 12. Process according toclaim 1, wherein said amount of said alkali metal hydroxide feed, whichis sufficient to achieve a substantial buffering effect, is a sodiumhydroxide feed of from about 0.5 kg/ton to about 5 kg/ton of drycellulose and said amount of said carbon dioxide feed, which issufficient to achieve a substantial buffering effect, is from about 0.5kg/ton to about 5 kg/ton of dry cellulose.
 13. A process for stabilizingthe pH of a pulp suspension at a desired pH level, comprising providinga papermaking pulp suspension and increasing the buffering ability ofsaid paper making pulp suspension by adding to the circulation system ofpulp and white water in the stock preparation of a paper machine in apaper mill, a combination of an alkali metal hydroxide feed and a carbondioxide feed, which feeds cooperate to increase the pH of said pulpsuspension and to otherwise only counter each other's PH adjustingeffects without further separate uses of their respective intermediatepH adjusting effects, each of said feeds being added in an amountgreater than what would be required to only adjust the pH of thesuspension to the desired pH level, said feeds being provided in anamount sufficient to achieve a significant buffering effect of said pulpsuspension and to increase the pH of said pulp suspension and maintainthe pH at a desired level from the addition of the feeds throughout theshort circulation and formation of the paper on the paper machine. 14.Process according to claim 13, wherein the step of providing said papermaking pulp suspension includes adding water to bales of pulp or addingwater to pulp of increased consistency coming from a pulp mill. 15.Process according to claim 13, wherein said amount of alkali metalhydroxide feed, which achieves a significant buffering, is a sodiumhydroxide feed of from about 0.5 kg/ton to about 5 kg/ton of drycellulose and said amount of carbon dioxide feed, which achieves asignificant buffering, is equal to from about 0.5 kg/ton to about 5kg/ton of dry cellulose.
 16. A process for stabilizing the pH of a pulpsuspension at a desired pH level, comprising providing a papermakingpulp suspension in a paper mill after a pulp mill and increasing thebuffering ability of said pulp suspension by adding thereto, in thestock preparation of a paper machine in said paper mill, a combinationof an alkali metal hydroxide feed and a carbon dioxide feed, which feedscooperate to increase the pH of said pulp suspension and to otherwiseonly counter each other's pH adjusting effects without further separateuses of their respective intermediate pH adjusting effects, each of saidfeeds being added in an amount greater than what would be required toonly adjust the pH of the suspension to the desired pH level, said feedsbeing provided in an amount sufficient to achieve a significantbuffering effect of said pulp suspension and to increase the pH of saidpulp suspension and maintain the pH at a desired level from the additionof the feeds throughout the short circulation and formation of the paperon the paper machine.
 17. A process according to claim 16, wherein saidfeeds are added to the circulation of pulp and white water of said papermachine.
 18. A process for producing paper comprising: providing a papermaking pulp suspension for processing in the stock preparation of apaper machine in a paper mill; increasing the buffering ability of saidpulp suspension by adding thereto in said stock preparation acombination of an alkali metal hydroxide feed and a carbon dioxide feed,which feeds cooperate to increase the pH of said pulp suspension and tootherwise only counter each other's pH adjusting effects without furtherseparate uses of their respective intermediate pH adjusting effects,each of said feeds being provided in an amount greater than thatrequired to only adjust the pH of the pulp suspension to a desiredlevel, and said feeds being provided in an amount sufficient to achievea substantial buffering effect of said pulp suspension and to increasethe pH of said pulp suspension and maintain the pH at a desired levelfrom the addition of the feeds throughout the short circulation and theformation of the pulp suspension into a web; and forming said pulpsuspension into a web, and drying said web to form paper.
 19. Processaccording to claim 18, characterized in that the pH of said pulpsuspension is increased to a desired value between 7 and
 9. 20. Processaccording to claim 1, further comprising the step of providing said pulpsuspension for processing in the stock preparation of said paper machinein said paper mill, said pulp suspension being provided with an initialpH level lower than said desired pH level.
 21. Process according toclaim 20, wherein the step of providing said pulp suspension includesadding water to bales of pulp or adding water to pulp of increasedconsistency coming from a pulp mill.
 22. Process according to claim 20,wherein said amount of alkali metal hydroxide feed which achieves asignificant buffering effect is a sodium hydroxide feed equal to between0.5 and 5 kg/ton dry cellulose and said amount of carbon dioxide feedwhich achieves a significant buffering effect is equal to between 0.5and 5 kg/ton dry cellulose.
 23. Process according to claim 18, whereinthe step of providing said paper making pulp suspension includes addingwater to bales of pulp or adding water to pulp of increased consistencycoming from a pulp mill.
 24. Process according to claim 18, wherein saidamount of said alkali metal hydroxide feed, which is sufficient toachieve a substantial buffering effect, is a sodium hydroxide feed offrom about 0.5 kg/ton to about 5 kg/ton of dry cellulose and said amountof said carbon dioxide feed, which is sufficient to achieve asubstantial buffering effect, is from about 0.5 kg/ton to about 5 kg/tonof dry cellulose.
 25. A process for producing paper comprising: (a)adding water to bales of pulp or to pulp of increased consistency from apulp mill to provide a paper making pulp suspension for processing inthe stock preparation of a paper machine in a paper mill including shortcirculation and formation of the pulp suspension into a web; (b)increasing the buffering ability of said pulp suspension in said stockpreparation by adding thereto a combination of an alkali metal hydroxidefeed and a carbon dioxide feed, which feeds cooperate to increase the PHof said pulp suspension and to otherwise only counter each other's pHadjusting effects without further separate uses of their respectiveintermediate pH adjusting effects, said feeds being provided in anamount greater than that required to only adjust the pH of the pulpsuspension to a desired level, and said feeds being provided in anamount sufficient to achieve a substantial buffering effect of said pulpsuspension and to increase the pH of said pulp suspension and maintainthe pH at a desired level from the addition of the feeds throughout theshort circulation and the formation of the pulp suspension into a web,and (c) forming said pulp suspension into a web, and drying said web toform paper.
 26. Process according to claim 25, wherein the amount ofsaid alkali metal hydroxide feed sufficient to achieve a substantialbuffering effect is a sodium hydroxide feed of from about 0.5 kg/ton toabout 5 kg/ton of dry cellulose and the amount of said carbon dioxidefeed sufficient to achieve a substantial buffering effect is from about0.5 kg/ton to about 5 kg/ton of dry cellulose.